1. Field of the Invention
Embodiments of the invention generally relate to a device that monitors and evaluates electrogram signals that represent electric activities of a heart chamber or intracardiac electrograms, such as atrial intracardiac electrograms.
2. Description of the Related Art
Intracardiac electrograms may be picked up by electrode leads or catheters that include one or more electrode poles that pick up electric potentials originating from the myocardium of a respective heart chamber (atrium or ventricle). Typically, myocardial cells depolarize and contract in response to natural or artificial stimulation. In a healthy heart chamber, depolarization of the muscle cells of the myocardium occurs nearly simultaneously leading to a contraction of the respective heart chamber. The change of electric potentials that co-occur with the depolarization and repolarization may be picked-up and form time-varying electrograms. In a certain time period after depolarization a muscle cell is unsusceptible for another stimulation. The time period is typically called refractory period of the muscle cell. In a healthy heart, electric conduction of stimulation pulses causes the myocardium to contract in a coordinated manner. However, if the electric conduction is affected, an uncoordinated contraction of muscle cells may occur wherein a part of the muscle cells contract while others already are refractory and become stimulated with a certain delay, which may lead to fibrillation of the affected heart chamber, for example AF (atrial fibrillation).
A means to prevent such disorganized electric conduction and depolarization is generally known as ablation whereby local lesions of the myocardial tissue are induced in order to interrupt electric conduction of stimuli at the sites of respective lesions. To determine myocardial sites to be treated by means of ablation, monitoring of the electric potentials in a heart chamber, also referred to as mapping, is carried out.
Complex fractionated atrial electrograms (CFAE) have been identified as targets for AF ablation. Several catheter-based cardiac mapping systems have been developed that incorporate the features to map and identify areas associated with CFAE, which may function either as the drivers or the necessary substrate required for AF maintenance. However, there is no universal agreement on the precise definition of CFAE.
For example, “A New Approach for Catheter Ablation of Atrial Fibrillation: Mapping of the Electrophysiologic Substrate”, a publication of the Journal of the American College of Cardiology (JACC) 2004, volume 43 pages 2044-2053, to Nademanee et al., presents CFAE-guided AF ablation in humans. According to Nademanee et al., CFAE is defined in two ways. One definition of CFAE is described as “fractionated electrograms composed of two deflections or more, and/or perturbation of the baseline with continuous deflection of a prolonged activation complex over a 10-s recording period.” Another definition is described as “atrial electrograms with a very short cycle length (≦120 ms) averaged over a 10-s recording period.”
“Stability of Complex Fractionated Atrial Electrograms”, a publication of the Journal of Cardiovascular Electrophysiology 2012, volume 23 pages 980-987, to Lau et al., shows a systematic review of several methods to define CFAE based on time domain measurement. According to Lau et al., one method defines CFAE as the mean of time intervals between the marked deflections being less than 120 ms. Another method of Lau et al. counts ICL (Interval Confidence Level), which is the number of intervals (usually of 50-120 ms) between tagged intrinsic local activations within a sampling period, and AIPI (Average Inter-Potential Interval), which refers to the average of all intervals between 2 successive tagged deflections of >50 ms. According to Lau et al., CFAE is defined by ICL≧5 and AIPI<100 ms. A third definition of CFAE is described in Lau et al. as the presence of 2 or more successive tagged deflections with interval <50 ms and expressed as number of deflections or percentage of continuous activity. Furthermore, a fourth definition of CFAE in Lau et al. is that the electrograms show atrial complexes of >50 ms with more than 3 deviations from baseline.
Besides the time domain methods, the CFAE is also defined based on dominant frequency (DF) analysis. The principle is to transform the signal from the time domain to the frequency domain. Subsequently, the highest peak in the spectrum is generally identified as the DF. The location with the highest DF value is subject to ablation. “Complex Fractionated Atrial Electrograms: Properties of Time-Domain Versus Frequency-Domain Methods”, a publication of the Heart Rhythm Journal 2009, volume 6 pages 1475-1482, to Grzeda et al., shows that the DF method appears to be more robust than the time-domain method in identifying the CFAE sites.
“Differences in Repeating Patterns of Complex Fractionated Left Atrial Electrograms in Longstanding Persistent as Compared with Paroxysmal Atrial Fibrillation”, a publication of the Circulation: Arrhythmia and Electrophysiology Journal 2011, volume 4 pages 470-477, to Ciaccio et al., extends the analysis of CFAE by focusing on the spatial and temporal repeatability of CFAE patterns. Ciaccio et al. appears to combine two independent methods, linear prediction and Fourier reconstruction, to quantify the repeatability of CFAE. According to Ciaccio et al., the degree of repeatability is site-specific and different in paroxysmal compared with longstanding AF.
“Measuring the Complexity of Atrial Fibrillation Electrograms”, a publication of the Journal of Cardiovascular Electrophysiology 2010, volume 21 pages 649-655, to Ng et al., evaluates Shannon's entropy (ShEn) and the Kolmogorov-Smirnov (K-S) test as statistical methods to quantify complexity of AF electrograms, and compares these measures with fractional intervals in distinguishing CFAE from non-CFAE signals. Ng et al. appears to show that ShEn could be used to automatically rank and classify CFAE electrograms, and has comparable performance to fractional intervals.
“Novel Assessment of Temporal Variation in Fractionated Electrograms Using Histogram Analysis of Local Fractionation Interval in Patients with Persistent Atrial Fibrillation”, a publication of the Circulation: Arrhythmia and Electrophysiology Journal 2012, volume 5 pages 949-956, to Lin et al. applies histogram analysis for substrate mapping in patients with persistent AF. Instead of relying on the mean fractionation interval (FI), Lin et al. appears to focus on evaluating the kurtosis and skewness of the FI histogram in order to characterize the temporal variation of the FI.
World Intellectual Property Organization Patent Publication 2012/021022 entitled “Simulated Arrhythmia Catheter Ablation System”, to Pak, presents a simulated arrhythmia catheter ablation system including a modeling unit, a pattern-producing unit, a mapping unit, an analysis unit, and a surgical unit. The modeling unit of Pak reproduces an atrial model by using heart image data. The pattern-producing unit produces an arrhythmia electrical-wave pattern on the atrial model. The mapping unit produces an atrial-site-specific electrical-signal map on the atrial model on which the arrhythmias electrical-wave pattern has been produced. The analysis unit discerns a core site of an electrical-wave vortex by using the atrial-site-specific electrical-signal map. The surgical unit carries out simulated catheter ablation at the core site of the electrical-wave vortex as discerned in the analysis unit.
United States Patent Publication 2007/197929 entitled “Mapping of Complex Fractionated Atrial Electrogram”, to Porath et al., discloses an apparatus and a method to automatically detect and map areas of complex fractionated electrograms. According to Porath et al., electrical signal data are obtained from respective locations of a heart and automatically analyzed to identify complex fractionated electrograms. Information derived from the signal data indicative of a spatial distribution of complex fractionated electrograms in a heart is displayed. Voltage peaks having amplitudes within a predefined voltage range may be identified and peak-to-peak intervals between the identified voltage peaks that occur within a predefined time range may be identified. Location information can be obtained using a position sensor. A functional map of a heart that is coded according to average or shortest durations of the complex fractionated electrograms or according to numbers of the complex fractionated electrograms detected in respective locations can be displayed.
U.S. Pat. No. 7,904,143 entitled “Binary Logistic Mixed Model for Complex Fractionated Atrial Electrogram Procedures”, to Ishay et al., shows methods and a medical apparatus for identifying CFAE locations. The method of Ishay et al. appears to locate an arrhythmogenic focus in a heart of a living subject by obtaining training electrical signal data from respective training locations of a training set of hearts, which are automatically analyzed to identify training complex fractionated electrograms (CFAEs) therein. A plurality of observers determines the medical significance of the CFAEs, which is recorded and a first estimation is generated at the respective training locations by fitting a mixed regression model to the training CFAEs and the determinations of medical significance. In a next step, patient electrical signal data from respective locations of a patient heart are obtained and automatically analyzed to identify CFAEs. The mixed regression model is applied on the CFAEs to obtain second estimations of medical significance and an indication that one or more of the respective locations of the patient heart are medically significant are displayed.
U.S. Pat. No. 8,315,696 entitled “Identifying Critical CFAE Sites Using Contact Measurement”, to Schwartz, shows a method and a mapping apparatus for mapping complex fractionated electrograms by a probe at respective locations in a chamber of a heart of a subject. The mapping apparatus of Schwartz includes a probe and a processor. The probe is configured to sense electrical activity in a chamber of a heart of a subject. The processor is configured to receive and process electrical inputs from the probe at multiple locations in the chamber. The processor identifies complex fractionated electrograms and measures at each location a respective contact quality between the probe and tissue in the chamber. The processor creates a map of the CFAE in the chamber using the electrical inputs and measured contact quality to distinguish between active and passive CFAEs. The apparatus may include an energy generator for ablation of sites at which CFAE were detected while contact quality satisfied a predetermined contact criterion.
Generally, it is likely that CFAE defined by different algorithms may represent different aspects of the underlying pathophysiology of atrial fibrillation (AF). For example, generally, it has been shown that there is poor anatomic overlap between CFAE defined by multi-component/continuous electrograms (EGMs) and CFAE defined by AF cycle length <120 ms, as disclosed by Lee et al. in “Relationship Among Complex Signals, Short Cycle Length Activity, and Dominant Frequency in Patients with Long-Lasting Persistent AF” published in the Heart Rhythm Journal 2011, volume 8 pages 1714-1719. Generally, most methods, including time domain methods and dominant frequency methods, characterize CFAE based on the fractionation intervals, ignoring information related to the amplitude variation of the electrograms. Other features of the electrogram morphology that reflect fractionated signal complex, such as the number of local peaks in a complex, the number of zero-crossings in a complex, the frequency content of a complex, or the like are generally also ignored.
Although the amplitude information is taken into consideration when quantifying the atrial electrogram complexity, as discussed in Ng et al. and Ciaccio et al., every data sample of the electrograms, including those in the signal baseline is included in the calculation, thus rendering these methods subject to the influence of recording noise, as well as the far-field components generated from distant atrial sites. Moreover, the clinical utility of these methods has not been confirmed.
As such, in view of the above, there is a need for a device for monitoring and evaluating electrogram signals representing electric activities of a heart chamber.